The present invention concerns routing of messages in an Internet Protocol (IP) Multimedia Subsystem (IMS) provided as part of 3GPP (Third Generation Partnership Program) UMTS (Universal Mobile Telecommunications System), as set out in various 3GPP specifications including 3GPP Technical Specification (TS) 23.228, “IP Multimedia Subsystem (IMS); Stage 2.” The IP Multimedia CN (core network) subsystem comprises all CN elements for provision of multimedia services, including the collection of signalling and bearer related network elements as defined in 3GPP TS 23.002. IP multimedia services are based on a session control capability defined by IETF (the Internet Engineering Task Force); the session control capability, along with multimedia bearers, utilizes the PS (packet-switched) domain, which may include services equivalent to some services in the CS (circuit-switched) domain.
To achieve access independence and to maintain a smooth interoperation with wireline terminals across the Internet, the IP multimedia subsystem attempts to conform to IETF Internet standards. Therefore, the interfaces specified conform as far as possible to IETF Internet standards for the cases where an IETF protocol has been selected, e.g. the so-called Session Initiation Protocol (SIP).
The IP multimedia core network (IM CN) subsystem, as described in 3GPP TS 23.228, includes inter alia one or another variety of CSCF (call state control function).
A UE (user equipment) uses SIP (Session Initiation Protocol) in communicating with IMS, and the IMS network (i.e. more specifically, the IM CN) is responsible for routing the SIP messages/requests to the recipients. In routing a message, the IMS uses the request URI (uniform resource identifier) of the message to find the S-CSCF (serving CSCF) serving the target user; that S-CSCF finally delivers the request e.g. to the target user (e.g. a terminating UE) via certain intermediate CSCF elements. The scheme of an address of a message, or more properly of the request URI of the message, is the part of the URI that tells a client (such as e.g. an HTML client or an XML client), such as a browser, which access method to use to access the resource specified in the URI, or in other words which protocol(s) to use. A scheme consists of a token followed by a colon and placed at the beginning of an address (e.g. ‘sip:’ or ‘wv:’ or ‘mailto:’ or ‘http:’).
As stated in RFC 3261 (“SIP: Session Initiation Protocol,” by the Network Working Group of the Internet Engineering Task Force, available on the Internet at http://www.faqs.org/rfcs/rfc3261.html), a request URI is a SIP URI or a SIPS URI (as described in Section 19.1 of RFC 3261) or a general URI (as defined in RFC 2396). A request URI indicates the user or service to which a request is being addressed. SIP elements may support request URIs with schemes other than “sip:” and “sips:” such as for example the “tel:” URI scheme of RFC 2806 (“URLs for Telephone Calls,” by the Network Working Group, available on the Internet at http://www.faqs.org/rfcs/rfc2806.html). SIP elements may translate non-SIP URIs using any mechanism at their disposal, resulting in a SIP URI, SIPS URI, or some other scheme.
The generic syntax for a SIP URI is defined in RFC 3261 and is as follows:
SIP-URI = “sip:” [ userinfo “@” ] hostport uri-parameters [ headers ]userinfo = [ user | telephone-subscriber [ “:” password ] ]hostport = host [ “:” port ]host = hostname | IPv4address | IPv6referencehostname = * ( domainlabel “.” ) toplabel [ “.” ]uri-parameters = * ( “;” uri-parameters )uri-parameter = transport-param / user-param / method-param / ttl-param / maddr-param / lr-param / other-paramtransport-param = “transport=” ( “udp” / “tcp” / “sctp” / “tls” / other-transport )other-transport = tokenuser-param = “user” ( “phone” / “ip” / other-user )other-user = token
For presence and (instant) messaging, IETF suggests the usage of protocol-agnostic schemes (meaning schemes that do not indicate a particular protocol) and provides ‘im:’ and ‘pres:’ as such schemes; (‘im:’ and ‘pres:’ are specified in draft-ietf-impp-cpim-03, not yet an RFC). The purpose of the schemes ‘im:’ and ‘pres:’ is to be able to address a target user (a publisher or recipient) without taking into account the communication technology (i.e. the communication protocols) the target user is using, or, more specifically, the communication protocol that is used to contact the server that in turn communicates with the target user using potentially yet another protocol, as set out in the above-mentioned draft-ietf-impp-cpim-03.
In IMS as specified by 3GPP Release 5, the use of SIP URIs with schemes other than ‘sip:’ and ‘tel:’ is not taken into account. Thus, it is not possible to handle SIP messages with schemes other than ‘sip:’ and ‘tel:’ properly in a 3GPP Release 5 compliant network.
More specifically, in a 3GPP Release 5 IMS network according to the prior art, an I-CSCF (Interrogating CSCF) server is responsible for finding the S-CSCF assigned to a target user (or resource) based on the request-URI, and the I-CSCF does so by querying an HSS (Home Subscriber Server) database; the I-CSCF assumes that the request URI can be matched to the information contained in the HSS database. Such a match occurs when the request-URI is a SIP URI representing some registered IMS user, but if the request-URI uses a protocol-agnostic scheme, there will be no match according to the prior art.
Assuming that the IMS allows an SIP message for a target user with a request URI using a non-SIP scheme to be routed up to the target-side I-CSCF (which the current Rel5 compatible IMS does not allow), what is still needed is a change to 3GPP-specified IMS allowing the use of protocol-agnostic schemes, i.e. a change resulting in a message having an address with a protocol-agnostic scheme being routed through the IMS up to either a border gateway or to the target user, and so allowing the routing of messages having other than “sip:” and “tel:” as schemes.